unary "-" operator

I don't know if this is something that's been argued before, but I
came across an interesting example of why the unary '-' is bad, while
searching for reasons that single line comments are bad. A section
involving the binary minus operator must always be bracketed, and as
such will always have a '(' infront of it. That means that this
example can never happen:
infixl 0 -->
(-->) x y = print x >> print y
f = do { -5 --> 5; return()}
Delete the space after the '{' and you have a problem. This can't
happen if you don't have a unary minus.
Bob